1. Field of the Invention
The present invention relates generally to a capacity control valve for variably modulating a capacity or a pressure of a process fluid in a control chamber of an air-conditioning system and its control method. More particularly, the invention relates to a capacity control valve and its control method in which a capacity or a pressure in a control chamber of a compressor is controlled with reference to the pressure load of the capacity control valve.
2. Description of the Related Art
There have been known as a relative art of the present invention capacity control valves for a variable displacement type swash plate compressor in an air-conditioning system. The relative art of the capacity control valve is illustrated in FIG. 8.
In FIG. 8, a pressure sensing element 210 is disposed in a suction chamber 206 which is located at a lower end of a capacity control valve 200. The pressure sensing element 210 is composed of a resilient bellows with a biasing spring 210A which is disposed inside the bellows and the element is constructed in such a way that an upper end of the element moves downward as a result of a contraction due to a suction pressure Ps supplied from an external. An intermediate rod 207 which is connected with an upper end of the pressure sensing element 210 is disposed in a guide hole of a housing 220 in an axially movable manner. Furthermore, a valve body 201 integrally connected to the intermediate rod 207 is disposed in a valve chamber 208, as shown in FIG. 8, at an upper portion of the housing 220. The valve body 201 moves upward or downward, which accordingly opens or closes the valve chamber 208 by lifting from or seating against a valve seat of a valve hole in the valve chamber 208.
The housing 220 has an intake port for a suction pressure Ps, an outlet port for a discharge pressure Pd, and an intake port of a crank chamber for a crack pressure Pc wherein the outlet port for the discharge pressure Pd is connected to the valve chamber 208 by means of a through communicating passage 209 as indicated by the dotted line. When the valve chamber 208 is opened by the valve body 201, the valve chamber 208 is directly connected to the intake port of the crank chamber for the crank pressure Pc via a valve hole and a fluid at the crank pressure Pc fluid flows into the crank chamber, which is not shown in FIG. 8.
In an opening or a closing of the valve body 201, the suction pressure of the pressure sensing element 210 is altered in accordance with the generated force of an electromagnetic solenoid coil section 202 which is disposed at an upper end portion of the capacity control valve 200, and a capacity control of the variable displacement compressor is achieved by adjusting the crank pressure Pc of the crank chamber by means of controlling an incoming flow of the discharge pressure Pd into the crank chamber in accordance with the degree of opening of the valve body 201 against a valve seat for a valve hole.
The pressure sensing element 210 disposed in the suction chamber 206 has a load characteristic such that the element expands or contracts in accordance with the suction pressure Ps within a normal use range of the suction pressure Ps.
When no electric current is supplied to the electromagnetic solenoid coil section 202, the valve body 201 is maintained at a fully opened position by an urging spring force of a return spring 203. This fully opened position corresponds to a fully unloaded operation state. When the current is supplied to the solenoid coil section 202, an electromagnetic attractive force is generated between a plunger 204 and a fixed iron core 205. The valve body 201 maintains its fully opened position, namely an insensitive range, until the electromagnetic force exceeds the opposing urging force of the return spring 203.
However, when an electromagnetic force exceeds the urging force of the return spring 203, a plunger rod 204A to push the valve body 201 in a direction of closing the valve, entering a control range of the suction pressure Ps. Within the control range, as a coil current becomes larger, a larger force to close the valve as well as a lower set value of the suction pressure Ps is resulted.
In this type of capacity control valve 200, it is difficult to quickly reduce a heavy cooling load because the valve relies on the suction pressure Ps. Consequently, the compressor has to be shut off by means of clutch and the air-conditioning system needs to be turned off. The on-off action of the clutch induces an abrupt torque change of the compressor, which requires more fuel consumption due to an increased engine power. This also affects a driving performance.
Furthermore, a variation in the crank pressure Pc due to the different operation modes of a compressor may cause inevitable disturbances to the suction pressure Pc. Therefore, an accurate current control of the electromagnetic solenoid coil is hard to achieve and precision of a capacity control is hardly improved by means of a specified suction pressure Ps.
For a capacity control valve 200 which adopts the suction pressure Ps as a control reference, when a set value of the suction pressure needs to be changed by means of the solenoid coil 202, a high susceptibility of the suction pressure to a thermal load of an evaporator worsens a response of the compressor in accordance with a change in the discharge amount. Under this circumstance, if the compressor rapidly increases its rotational speed, a change in the discharge cannot keep up with such a sudden change, which results in a temporary increase of a pressure load onto the compressor, which may in turn cause an inaccurate action of the capacity control valve and loss of energy.
As a capacity control valve based on suction pressure Ps has a difficulty in rapidly modulating a control chamber pressure, incorporation of a clutch is required for a variable displacement compressor, for instance, which causes noise during its operations. Furthermore, a torque increase due to the ON-OFF action of the clutch is likely to impose further difficulty on an accurate capacity control.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to realize an accurate control of the pressure or the capacity of a capacity control valve by means of a solenoid coil section via a highly responsive fluid pressure without being affected by an engine speed or peripheral temperature characteristics.
Another goal is to achieve a stable control of a capacity control valve according to a specified pressure load with no fluctuation of the pressure load and to prevent loss of rotary torques.